U.S. patent application number 09/837105 was filed with the patent office on 2001-11-01 for self-light emitting device and electrical appliance using the same.
This patent application is currently assigned to Semiconductor Energy Laboratory Co., Ltd.. Invention is credited to Kimura, Hajime.
Application Number | 20010035713 09/837105 |
Document ID | / |
Family ID | 18632417 |
Filed Date | 2001-11-01 |
United States Patent
Application |
20010035713 |
Kind Code |
A1 |
Kimura, Hajime |
November 1, 2001 |
Self-light emitting device and electrical appliance using the
same
Abstract
A self-light emitting device and an electrical appliance
including the same are provided, in which extracting efficiency of
light from a light emitting element, especially in an EL element,
can be improved. A light scattering body formed by etching a
transparent film is provided on an insulator so that the extracting
efficiency of light can be improved, and the self-light emitting
device with high efficiency of light emission can be provided.
Inventors: |
Kimura, Hajime; (Kanagawa,
JP) |
Correspondence
Address: |
COOK, ALEX, McFARRON, MANZO,
CUMMINGS & MEHLER, LTD.
SUITE 2850
200 WEST ADAMS STREET
CHICAGO
IL
60606
US
|
Assignee: |
Semiconductor Energy Laboratory
Co., Ltd.
|
Family ID: |
18632417 |
Appl. No.: |
09/837105 |
Filed: |
April 18, 2001 |
Current U.S.
Class: |
313/501 ;
257/E33.074; 313/506 |
Current CPC
Class: |
H01L 51/5268 20130101;
H01L 27/3246 20130101; H01L 27/3283 20130101; H01L 27/3281
20130101; H01L 27/3244 20130101 |
Class at
Publication: |
313/501 ;
313/506 |
International
Class: |
H01J 001/62 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 21, 2000 |
JP |
2000-121854 |
Claims
What is claimed is:
1. A self-light emitting device comprising: a light emitting
element; a light scattering body; and an insulator interposed
between the light emitting element and the light scattering
body.
2. A self-light emitting device comprising: a first electrode
formed on an insulator; an EL layer formed on the first electrode;
a second electrode formed on the EL layer; and a light scattering
body formed at a side opposite to the first electrode through the
insulator, wherein said first electrode is electrically connected
to a TFT.
3. The self-light emitting device according to claim 2, wherein the
first electrode is an anode, and the second electrode is a
cathode.
4. The self-light emitting device according to claim 2, wherein the
first electrode comprises a translucent material, and the second
electrode comprises a light shielding material.
5. A self-light emitting device comprising: a first electrode
formed on an insulator; an EL layer formed on the first electrode;
a second electrode formed on the EL layer; and a light scattering
body formed at a side opposite to the first electrode through the
insulator.
6. The self-light emitting device as according to claim 5, wherein
the first electrode is an anode, and the second electrode is a
cathode.
7. The self-light emitting device according to claim 5, wherein the
first electrode comprises material, and the second electrode
comprises a light shielding material.
8. The self-light emitting device according to claim 1, wherein the
light scattering body comprises a translucent material.
9. The self-light emitting device according to claim 2, wherein the
light scattering body comprises a translucent material.
10. The self-light emitting device according to claim 5, wherein
the light scattering body comprises a translucent material.
11. The self-light emitting device according to claim 1, wherein
the light scattering body comprises one selected from the group
consisting of polycarbonate, polyimide, BCB, indium oxide, and tin
oxide.
12. The self-light emitting device according to claim 2, wherein
the light scattering body comprises one selected from the group
consisting of polycarbonate, polyimide, BCB, indium oxide, and tin
oxide.
13. The self-light emitting device according to claim 5, wherein
the light scattering body comprises one selected from the group
consisting of polycarbonate, polyimide, BCB, indium oxide, and tin
oxide.
14. The self-light emitting device according to claim 1, wherein a
thickness (H) of the light scattering body has a relation of
H.gtoreq.W1 with respect to a pitch (W1) of the light scattering
body.
15. The self-light emitting device according to claim 2, wherein a
thickness (H) of the light scattering body has a relation of
H.gtoreq.W1 with respect to a pitch (W1) of the light scattering
body.
16. The self-light emitting device according to claim 5, wherein a
thickness (H) of the light scattering body has a relation of
H.gtoreq.W1 with respect to a pitch (W1) of the light scattering
body.
17. The self-light emitting device according to claim 1, wherein a
pixel pitch is at least twice as long as a pitch of the light
scattering body.
18. The self-light emitting device according to claim 2, wherein a
pixel pitch is at least twice as long as a pitch of the light
scattering body.
19. The self-light emitting device according to claim 5, wherein a
pixel pitch is at least twice as long as a pitch of the light
scattering body.
20. The self-light emitting device according to claim 1, wherein an
angle between the light scattering body and the insulator is not
less than 60.degree. and is less than 180.degree..
21. The self-light emitting device according to claim 2, wherein an
angle between the light scattering body and the insulator is not
less than 60.degree. and is less than 180.degree..
22. The self-light emitting device according to claim 5, wherein an
angle between the light scattering body and the insulator is not
less than 60.degree. and is less than 180.degree..
23. An electrical appliance using a self-light emitting device
according to claim 1.
24. An electrical appliance using a self-light emitting device
according to claim 2.
25. An electrical appliance using a self-light emitting device
according to claim 5.
26. A self-light emitting device comprising: a first electrode
formed on an insulator; an EL layer formed on the first electrode;
a second electrode formed on the EL layer; and a light scattering
body formed on the surface facing a material with the lowest
refractive index.
27. The self-light emitting device according to claim 26, wherein
the first electrode is an anode, and the second electrode is a
cathode.
28. The self-light emitting device according to claim 26, wherein
the first electrode is a cathode, and the second electrode is an
anode.
29. The self-light emitting device according to claim 26, wherein
the light scattering body comprises a translucent material.
30. The self-light emitting device according to claim 26, wherein
the light scattering body comprises one selected from the group
consisting of polycarbonate, polyimide, BCB, indium oxide, and tin
oxide.
31. The self-light emitting device according to claim 26, wherein a
thickness (H) of the light scattering body has a relation of
H.gtoreq.W1 with respect to a pitch (W1) of the light scattering
body.
32. The self-light emitting device according to claim 26, wherein a
pixel pitch is at least twice as long as a pitch of the light
scattering body.
33. The self-light emitting device according to claim 26, wherein
an angle between the light scattering body and the insulator is not
less than 60.degree. and is less than 180.degree..
34. An electrical appliance using a self-light emitting device
according to claim 26.
35. The self-light emitting device according to claim 26, wherein
the first electrode is electrically connected to a TFT.
36. The self-light emitting device according to claim 26, wherein
the material with the lowest refractive index is the air.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an elemental device
structure for improving extracting efficiency of light produced in
the inside of an EL (electro luminescence) element when planar
light emission is extracted by supplying current to the EL element.
A self-light emitting device according to the present invention
includes an organic EL display and an OLED (Organic Light Emitting
Diode).
[0003] 2. Description of the Related Art
[0004] Although light emitted from a self-light emitting device is
extracted as planar light emission into the air, a lot of light can
not be extracted from the inside of the substrate since a substrate
positioned at an interface between the self-light emitting device
and the air has a flat plate shape, and its extracting efficiency
is 20 to 50%.
SUMMARY OF THE INVENTION
[0005] The present invention has been made to solve the above
problem, and an object of the invention is therefore to improve
extracting efficiency of light produced in a light emitting
element, especially in an EL element, by forming an uneven light
scattering body on the opposite surface of a substrate. Further,
the light scattering body is formed by etching a transparent film
on the substrate, and minute processing of pitches becomes
possible. Another object of the present invention is to provide a
self-light emitting device with higher efficiency of light emission
by forming a light scattering body of a minute pitch.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIGS. 1A to 1C are views showing a structure of a light
scattering body of the present invention.
[0007] FIG. 2 is an explanatory view of refraction of light.
[0008] FIGS. 3A to 3D are views in which the present invention is
used for an active matrix type TFT.
[0009] FIGS. 4A to 4G are views showing the details of light
scattering bodies.
[0010] FIGS. 5A to 5D are views in which the present invention is
used for an active matrix type TFT.
[0011] FIGS. 6A and 6B are views in which the present invention is
used for a reverse stagger active matrix type TFT.
[0012] FIGS. 7A to 7C are views in which the present invention is
used for a passive matrix type TFT.
[0013] FIGS. 8A to 8C are views in which the present invention is
used for a passive matrix type TFT.
[0014] FIGS. 9A to 9C are views in which the present invention is
used for a front light.
[0015] FIGS. 10A to 10C are views in which the present invention is
used for, a back light.
[0016] FIGS. 11A and 11B are views in which the present invention
is used for a front light and a back light.
[0017] FIGS. 12A and 12B are a view showing a structure of
connection of an EL element and a current controlling TFT, and a
view showing current-voltage characteristics of the EL element and
the current controlling TFT.
[0018] FIG. 13 is a view showing current-voltage characteristics of
an EL element and a current controlling TFT.
[0019] FIG. 14 is a view showing a relation between a gate voltage
and a drain current of a current controlling TFT.
[0020] FIGS. 15A to 15F are views showing examples of electrical
appliances.
[0021] FIGS. 16A and 16B are views showing examples of electrical
appliances.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] A configuration used for improving extracting efficiency of
light in the present invention will be described with reference to
FIGS. 1A to 1C.
[0023] FIG. 1A shows an example of a case in which the present
invention is used for an active matrix type self-light emitting
device. Reference numeral 101 designates a substrate made of an
insulator, and a current controlling TFT 102 is formed on the
substrate 101. A drain region of the current controlling TFT 102 is
electrically connected to a pixel electrode 103. (The pixel
electrode 103 can also be connected to a source region.) Here, the
pixel electrode 103 is an anode, and the pixel electrode 103 is
formed of a transparent conductive film so that light is emitted
from the side of the pixel electrode 103 of an EL element 106.
[0024] Further, an EL layer 104 is formed on the pixel electrode
103, and a cathode 105 is formed on the EL layer 104. Accordingly,
the EL element 106 constituted of the pixel electrode 103, the EL
layer 104, and the cathode 105 is formed.
[0025] In the self-light emitting device with the foregoing
configuration, unevenness is formed on a rear surface of the
substrate 101, that is, a surface at the side where the TFT is not
formed. A part of a light scattering body 108 is designated by 107,
and the enlarged view of the part 107 is shown.
[0026] With forming the light scattering body 108, it is possible
to prevent an incident angle from the light scattering body 108 to
the air 109 from exceeding the critical angle, and it is possible
to prevent light from being totally reflected and being confined in
the light scattering body. Thus, the extracting efficiency of light
from the EL element 106 can be improved. The light scattering body
is formed by etching a transparent film made of a transparent
material. In the present specification, the transparent film is a
film being transparent to visible light.
[0027] The enlarged view of the part 107 shown in FIG. 1B shows a
state where light which has passed through the substrate 101 passes
through the light scattering body 108 and is emitted into the air
109.
[0028] Light scattering bodies 108a, 108b, 108c, 108d and 108e
shown in FIG. 1B are respectively formed to be dot-shaped, and
these are called the light scattering body 108 in the present
specification.
[0029] FIG. 1C is a perspective view of a surface on which the
light scattering body 108 is formed.
[0030] In the present invention, light emitted from the EL element
106 enters the substrate 101, and then enters the light scattering
body 108.
[0031] Incidentally, as shown in FIG. 2, refraction of light is
determined by an angle (incident angle) of incident light and a
refractive index of a medium. Further, and follows a following
expression (Snell's law).
[0032] That is, in a medium 1 (201) with a refractive index
n.sub.1, when light (incident light) enters at an angle
.theta..sub.1 into a medium 2 (202) with a refractive index
n.sub.2, it becomes light (refracted light) of an angle
.theta..sub.2 satisfying the following expression
n.sub.1sin .theta..sub.1=n.sub.2sin .theta..sub.2 [Expression
1]
[0033] Incidentally, an incident angle .theta..sub.1 when an angle
.theta..sub.2 of refracted light becomes 90 is referred to as a
critical angle. When the incident angle .theta..sub.1 to the medium
2 becomes larger than the critical angle, light is totally
reflected. That is, light is confined in the medium 1.
[0034] Further, expressions (Fresnell's law) shown below are
established between reflectivity (R) and transmissivity (T) of
energy.
R=1/2{sin.sup.2(.theta..sub.1-.theta..sub.2)/sin.sup.2(.theta..sub.1+.thet-
a..sub.2)+tan.sup.2(.theta..sub.1-.theta..sub.2)/tan.sup.2(.theta..sub.1+.-
theta..sub.2)} [Expression 2]
T=1-R [Expression 3]
[0035] That is, if the refractive index of the substrate 101 is
different from that of the light scattering body 108, a reflection
component is generated. Thus, it is proper that the refractive
index of the substrate 101 is the same as that of the light
scattering body 108.
[0036] From the expressions 1 to 3, as shown in FIG. 1, when light
goes out into the air 109 with a refractive index of 1 from the
light scattering body 108 with a refractive index of 1.45 to 1.60,
that is, when light goes out into a medium with a small refractive
index from a medium with a large refractive index, the reflectivity
becomes large. When the incident angle becomes larger than the
critical angle, light is totally reflected. That is, it is
appropriate that the configuration of the light scattering body 108
is made so that the incident angle becomes small.
[0037] From the above, in the present invention, the configuration
of a light refraction layer is made uneven so that an incident
angle to the air becomes small, and more light is scattered and
becomes easy to extract into the air.
[0038] In the present invention, since irregular unevenness formed
by etching become the light scattering body 108, there is a merit
that it is not necessary to precisely unify the configuration and
preparation is easy.
[0039] Although the present invention can be used for many
self-light emitting devices, especially in an EL element using an
EL material which remarkably is subject to an influence of use
efficiency of light, since electric power consumed by the EL
element can be reduced and the life thereof can be lengthened, the
present invention is very effective.
[0040] Hereinafter, embodiments of the present invention will be
described in detail.
Embodiment 1
[0041] In this embodiment, a description will be given about an
example in which the present invention is used for an active matrix
type self-light emitting device in which light is transmitted to
the side of a pixel electrode. First, as shown FIG. 3A, a
transparent film is formed on a rear surface of a substrate 301. As
a transparent material for forming the transparent film, an organic
resin such as polycarbonate, acryl resin, polyimide, polyamide or
BCB (benzocyclobutene), indium oxide, tin oxide, or zinc oxide is
used, or a compound film of a combination of the above material is
used.
[0042] Next, this transparent film is etched, so that a light
scattering body 302 as shown in FIG. 3A is formed. The light
scattering body 302 formed at this time will be described with
reference to FIG. 4A. FIG. 4A shows the light scattering body 302
formed into a trapezoid. Since symbols used here are the same as
those used in FIG. 3A, correspondence may be made each time.
[0043] FIG. 4A shows an upside-down structure of FIG. 3A so that
the light scattering body 302 formed on the rear surface of the
substrate is positioned under the substrate. It is assumed that
light emitted from an EL element at a TFT side seen from the
substrate 301 enters the light scattering body 302 at an incident
angle .theta.1 as shown in FIG. 4A. Here, when the refractive index
of the substrate 301 is n1, and the refractive index of the light
scattering body 302 is n2, the light enters the light scattering
body 302 at an angle of .theta.2 if the relation of n1>n2 is
established.
[0044] On the other hand, if the relation of n1<n2 is
established, the light goes out into the light scattering body 302
at an angle of .theta.2'. That is, the relation of
.theta.2>.theta.2' is established, and the outgoing angle of
light going out into a medium with a high refractive index from a
medium with a low refractive index becomes small.
[0045] However, here, when the light is extracted from the light
scattering body 302 into the air, the outgoing angle becomes large,
the reflectivity also becomes high, and accordingly the outgoing
becomes difficult since the light goes out into a medium with a low
refractive index from a medium with a high refractive index. Then,
as shown in FIG. 4A, angles .theta.3 and .theta.4 between the light
scattering body 302a and the substrate of the insulator are
restricted. The present invention provide such a configuration that
the extracting efficiency of outgoing light in the normal direction
to the substrate in which the extracting efficiency is highest is
not dropped, and formation is made so that the angles .theta.3 and
.theta.4 become 60 degrees or larger. However, .theta.3 and
.theta.4 may not necessarily be formed to be the same angle.
[0046] Besides, in order to prevent an image from blurring, a pitch
of the light scattering body 302a is made such that a length W1 of
a contact portion to the substrate becomes a half of a pixel pitch
or less. Besides, in order to extract light more easily, the
shorter a length W2 of the trapezoid is, the better. Incidentally,
it is most desirable that W2=0.
[0047] Further, in order to form the light scattering body so that
the angles .theta.3 and .theta.4 of the light scattering body 302
become 60 degrees or larger, it is preferable that the thickness H
of the transparent film is made to have a relation of H.gtoreq.W1
with respect to the pitch (W1) of the light scattering body
302.
[0048] Besides, in the present invention, it is not necessary to
form an accurate configuration by using a metal mold or the like or
to smoothen the surface, but minute unevenness have only to be
formed on the rear surface of the substrate at the side where light
goes out.
[0049] In the manner as described above, the light scattering body
302 is formed on the rear surface of the substrate 301.
[0050] FIGS. 4B to 4G shows patterns which can be formed as the
light scattering body 302. FIG. 4B shows an example in which square
light scattering bodies are provided at intervals on the rear
surface of the substrate. FIG. 4C shows an example in which light
scattering bodies completely cover the substrate and there is no
interval between the light scattering bodies. FIG. 4D shows an
example in which reversed taper-shaped light scattering bodies are
formed on the rear surface of the substrate, and FIG. 4E shows an
example in which hemispheric light scattering bodies are formed on
the rear surface of the substrate. FIG. 4F shows elliptical light
scattering bodies, and FIG. 4G shows an example in which triangular
scattering bodies in section are formed.
[0051] Incidentally, the light scattering bodies shown in FIGS. 4A
to 4G may be provided so that intervals between the light
scattering bodies are secured, or the light scattering bodies
overlap with one another.
[0052] After the light scattering body 302 is formed on the rear
surface of the substrate 301, p-channel TFTs 303 and 304 are formed
by a well-known method on the surface of the substrate 301 on which
an insulating film is formed. Although the planar TFT is
exemplified in this embodiment, the TFT structure is not limited.
That is, a reverse stagger type TFT may be used.
[0053] Next, pixel electrodes 305 and 306 electrically connected to
the respective p-channel TITs 303 and 304 are formed. As the pixel
electrodes 305 and 306, a material with large work function is used
since they function as anodes of EL elements. Thus, in this
embodiment, as a translucent material (or transparent material)
which is transparent to visible light, an oxide conductive film (a
film made of indium oxide, tin oxide, or zinc oxide, or a compound
film of a combination of these) is used. Gallium may be added to
this oxide conductive film (FIG. 3B).
[0054] Next, banks 307 and 308 are formed of resin films so as to
surround the pixel electrodes 305 and 306, and an EL layer 309 is
formed thereon. In this embodiment, the banks 307 and 308 are
formed of acryl films, and the EL layer 309 is formed by a spin
coating method. As a material of the EL layer 309, polyfluorene of
a high molecular organic material is used. Of course, chromaticity
control may be made by adding a fluorescent material to
polyfluorene (FIG. 3C).
[0055] Next, a cathode is formed using a light-shielding material.
In this embodiment, as a cathode 311, an alloy film is formed to a
thickness of 300 nm by evaporating both aluminum and lithium, and a
silicon nitride film as a passivation film 312 is formed thereon by
a sputtering method. It is also effective to laminate a carbon
film, specifically a DLC (Diamond-Like Carbon) film thereon.
[0056] In the manner as described above, the self-light emitting
device having the structure shown in FIG. 3D is completed.
Thereafter, the EL element is sealed with resin or the EL element
is sealed in an airtight space so that the EL element does not come
in contact with the outer air.
Embodiment 2
[0057] In this embodiment, a description will be given of an
example in which the present invention is applied to an active
matrix type self-light emitting device which reflects light at a
side of a pixel electrode. First, as shown FIG. 5A, n-channel TFTs
502 and 503 are formed by a well-known method on a substrate 501
with an insulating film on its surface. In this embodiment,
although a planar type TFT is exemplified, a TFT structure is not
limited. That is, a reverse stagger type TFT may be used.
[0058] At this time, in the respective n-channel TFTs 502 and 503,
drain wiring lines are used as pixel electrodes 504 and 505. In the
case of this embodiment, since it is necessary for the pixel
electrodes 504 and 505 to reflect light, a metal film with high
reflectivity is used for the pixel electrodes 504 and 505. At the
same time, they also function as cathodes of EL elements, the metal
film containing a material with small work function is used. In
this embodiment, an alloy film containing aluminum and lithium is
used (FIG. 5A).
[0059] Next, banks 506 and 507 are formed of resin films so as to
surround the end portions of the pixel electrodes 504 and 505, and
an EL layer 508 is formed thereon. In this embodiment, the banks
506 and 507 are formed of acryl films, and the EL layer 508 is
formed by an evaporation method. As the material of the EL layer
508, Alq.sub.3 (tris-8-quinolinolato aluminum complex) is used. Of
course, chromaticity control may be made by adding a fluorescent
material to Alq.sub.3 (FIG. 5B).
[0060] Next, as an anode 510, an oxide conductive film in which
gallium oxide is added to zinc oxide is formed to a thickness of
300 nm, and further, as a passivation film 511, a silicon nitride
film is formed thereon by a sputtering method. It is also effective
to laminate a carbon film, specifically a DLC (Diamond-Like Carbon)
film thereon (FIG. 5C).
[0061] Next, as shown in FIG. 5D, a sealing film made of organic
resin is formed. At this time, the sealing film is formed so that
the EL element does not come in contact with the outer air.
[0062] Further, a sealing substrate 513 is provided on the sealing
film 512. At this time, the sealing substrate 513 is provided so
that the EL element does not come in contact with the outer air as
well as the formation of the sealing.
[0063] Next, a transparent film is formed on the sealing substrate.
As the transparent material for forming the transparent film,
organic resin such as polycarbonate, acryl resin, polyimide,
polyamide or BCB (benzocyclobutene); indium oxide, tin oxide, or
zinc oxide is used to form a film, or a compound film of a
combination of these is used. In order that angles .theta.3 and
.theta.4 of the light scattering body 514 becomes 60 degrees or
larger, it is preferable that the thickness (H) of the transparent
film is made to have the relation of H.gtoreq.W1 with respect to
the pitch (W1) of the light scattering body. By etching the
transparent film, the light scattering body 514 as shown in FIG. 5E
is formed.
[0064] It is not always necessary to provide the sealing film
formed of the organic resin film as shown in this embodiment, and
the EL element may be sealed in an airtight space. Incidentally,
since it becomes hard for light to be extracted when it goes out
into a medium with a low refractive index from a medium with a high
refractive index, in this case, it is appropriate that the light
scattering body 514 is provided on an interface between the
passivation film 511 and the airtight space, that is, on the
passivation film 511.
[0065] In the thus obtained self-light emitting device, since the
light scattering body is provided on the surface where light goes
out as compared with a normal sealing structure, high extracting
efficiency of light can be obtained as compared with a conventional
self-light emitting device. By this, since voltage for driving the
EL element can be made low, the life of the EL element can be
lengthened.
[0066] Incidentally, the structure of this embodiment can be put
into practice by combination with any structure of the embodiment
1.
Embodiment 3
[0067] In the embodiment 1 and the embodiment 2, although the
examples in which the present invention is applied to the planar
type TFT have been described, in this embodiment, a structure in
which the present invention is used for a reverse stagger type TFT
is shown in FIGS. 6A and 6B.
[0068] FIG. 6A shows a structure of an active matrix type
self-light emitting device in which light is transmitted to the
side of a pixel electrode, and FIG. 6B shows a structure of an
active matrix type self-light emitting device in which light is
reflected at the side of a pixel electrode.
[0069] In FIGS. 6A and 6B, reference numeral 601 designates a
substrate; 602, a p-channel TFT' used in FIG. 6A; and 603, an
n-channel TFT used in FIG. 6B. In either case, a gate electrode is
formed on the substrate 601, and a source region, a drain region
and a channel formation region are formed on the gate electrode
through a gate insulating film. Reference numeral 604 designates a
pixel electrode; and 605, a bank partitioning the pixel electrode.
An EL layer 606 is formed on the pixel electrode 604, and a cathode
607 and a passivation film 608 are formed on the EL layer 606.
[0070] Incidentally, since FIG. 6A shows the structure in which
light is transmitted to the side of the pixel electrode, a light
scattering body 609 is provided on the rear surface of the
substrate 601. Since FIG. 6B shows the structure in which light is
reflected at the side of the pixel electrode, the light scattering
body is formed on a sealing structure made of a sealing film 610
and a sealing substrate 611 on the passivation film 608.
[0071] Since the reverse stagger type TFT structure can be more
easily fabricated than the planar type TFT, the number of masks can
be reduced. Further, since the gate insulating film and the channel
formation region can be continuously formed, there is a merit that
the interface can be formed without being polluted.
[0072] The structure of this embodiment can be freely combined with
any structure of the embodiment 1 and the embodiment 2 and can be
put into practice.
Embodiment 4
[0073] In this embodiment, a description will be given on an
example in which the present invention is applied to a passive
matrix type self-light emitting device which radiates light through
a substrate.
[0074] First, a transparent film is formed on a rear surface of a
substrate 701. As the transparent material for forming the
transparent film, organic resin such as polycarbonate, acryl resin,
polyimide, polyamide or BCB (benzocyclobutene); indium oxide, tin
oxide, or zinc oxide is used to form a film, or a compound film of
a combination of these is used. In order to form a light scattering
body so that angles of .theta.3 and .theta.4 of a light scattering
body 702 becomes 60 degrees or larger, it is preferable that the
thickness (H) of the transparent film is made to have the relation
of H.gtoreq.W1 with respect to the pitch (W1) of the light
scattering body.
[0075] By etching this transparent film, a trapezoid light
scattering body 702 as shown in FIG. 7A is formed. At the time of
etching, it is necessary to prevent the transparent film from being
excessively etched so that the substrate 701 is exposed on the
surface. This is because if the substrate is exposed on the
surface, refraction of light by the light scattering body 702 comes
not to be sufficiently made.
[0076] Next, the substrate 701 shown in FIG. 7A is turned upside
down, and the surface of the substrate 701 is made the upside.
After an insulating film is formed on the surface of the substrate
701, an anode 703 is formed on the insulating film. In this
embodiment, as the anode 703, an oxide conductive film made of a
compound of indium oxide and tin oxide is used (FIG. 7B).
[0077] This anode 703 is formed like a band in the parallel
direction with the paper surface, and it is arranged like a stripe
in the normal direction to the paper surface. This structure is
same as a well-known passive matrix type self-light emitting
device.
[0078] Next, a partition wall 704 is formed to intersect the anode
703 at right angles. The partition wall 704 is provided to separate
a metal film which becomes a cathode. In this embodiment, a
two-layer resin film is used, and it is processed to form a T
shape. The structure like this can be obtained by carrying out
etching under the condition that an etching rate of a lower layer
is faster than that of an upper layer.
[0079] Next, an EL layer 705 is formed. In this embodiment, the EL
layer 705 is formed by an evaporation method. As the material of
the EL layer 705, Alq.sub.3 (tris-8-quinolinolato aluminum complex)
of a low molecular organic material is used. Of course,
chromaticity control may be performed by adding a fluorescent
material to Alq.sub.3.
[0080] Next, as a cathode 707, an alloy film is formed to a
thickness of 300 nm by evaporating both aluminum and lithium. At
this time, the cathode 707 is separated along the partition wall
704, is formed like a band in the normal direction to the paper
surface, and is arranged like a stripe. Further, as a passivation
film 708, a resin film is formed thereon by an ink jet method or a
printing method. It is also effective to laminate a carbon film,
specifically a DLC (Diamond-Like Carbon) film thereon.
[0081] With the manner as described above, the self-light emitting
device with the structure shown in FIG. 7C is completed.
Thereafter, an EL element is sealed with resin so that the EL
element does not come in contact with the outer air.
[0082] In the thus obtained self-light emitting device, since the
light scattering body is provided on the outgoing surface of light
as compared with a normal sealing structure, high extracting
efficiency of light can be obtained as compared with a conventional
self-light emitting device. Accordingly, since a voltage for
driving an EL element can be made lower than a normal voltage, the
life of the EL element can be lengthened.
[0083] The structure of this embodiment can be combined with any
structure of the embodiments 1 to 3 and can be put into
practice.
Embodiment 5
[0084] In this embodiment, a description will be given on an
example in which the present invention is applied to a passive
matrix type self-light emitting device which radiates light upward
with respect to a substrate. First, a cathode 802 is formed on a
substrate 801 on which an insulating film is formed. In this
embodiment, as the cathode 802, an electrode with a structure in
which a MgAg film (metal film obtained by evaporating both
magnesium and silver) is laminated on an aluminum film is used
(FIG. 8A).
[0085] This cathode 802 is formed into a band shape in the parallel
direction to the paper surface, and it is arranged in a stripe
shape in the normal direction to the paper surface.
[0086] Next, a partition wall 803 is formed to intersect the
cathode 802 at right angles. The partition wall 803 is provided to
separate an oxide conductive film which becomes an anode. In this
embodiment, a two-layer resin film is used and is processed to form
a T shape. The structure like this can be obtained by carrying out
etching under the condition that an etching rate of a lower layer
is faster than that of an upper layer.
[0087] Next, an EL layer 804 is formed. In this embodiment, the EL
layer 804 is formed by an evaporation method. As the material of
the EL layer 804, Alq.sub.3 (aluminum quinolinolato complex) of a
low molecular material is used. Of course, chromaticity control may
be performed by adding a fluorescent material to Alq.sub.3.
[0088] Next, as an anode 806, an oxide conductive film made of a
compound of indium oxide and zinc oxide is formed to a thickness of
300 nm. At this time, the anode 806 is separated along the
partition wall 803, is formed like a band in the normal direction
of the paper surface, and is arranged like a stripe. Further, as a
passivation film 807, a resin film is formed thereon by an ink jet
method or a printing method. It is also effective to laminate a
carbon film, specifically a DLC (Diamond-Like Carbon) film
thereon.
[0089] With the manner as described above, the structure shown in
FIG. 8B is formed, and then, an EL element is sealed with resin so
that the EL element does not come in contact with the outer air,
and a sealing film 808 is formed. Further, a sealing substrate 809
is provided on the sealing film 808.
[0090] Next, a transparent film is formed on the sealing substrate
809. As the material for forming the transparent film, organic
resin such as polycarbonate, acryl resin, polyimide, polyamide or
BCB (benzocyclobutene), indium oxide, tin oxide, or zinc oxide is
used to form a film, or a compound film of a combination of these
is used. In order to form the light scattering body so that the
angles of .theta.3 and .theta.4 of the light scattering body 810
become 60 degrees or larger, it is preferable that the thickness
(H) of the transparent film is made to have the relation of
H.gtoreq.W1 with respect to the pitch (W1) of the light scattering
body. By etching this transparent film, a light scattering body 810
shown in FIG. 8C is formed.
[0091] As described above, by forming the light scattering body 810
with the minute structure on the surface where light goes out, it
becomes possible to extract light produced from the EL element more
effectively.
[0092] It is not always necessary to provide the sealing film
formed of the organic resin film as shown in this embodiment, and
the EL element may be sealed in an airtight space. Incidentally,
since it becomes hard for light to be extract when it goes out from
a medium with a high refractive index into a medium with a low
refractive index, in this case, the light scattering body is
provided on an interface between the passivation film 807 and the
airtight space, that is, on the passivation film 807, and the
sealing substrate 809 is provided over the airtight space.
[0093] In the thus obtained self-light emitting device, since the
light scattering body is provided on the surface where light goes
out as compared with a normal sealing structure, the extracting
efficiency of light can be raised as compared with a conventional
self-light emitting device. Accordingly, since a voltage for
driving the EL element can be made lower than that in a normal
case, the life of the EL element can be lengthened.
[0094] The structure of this embodiment can be combined with any
structure of the embodiments 1 to 4 and can be put into
practice.
Embodiment 6
[0095] Next, an example in which the present invention is used for
a front light will be described. FIGS. 9A to 9C are views showing
the structure of a front light. FIGS. 9A and 9B show sections of
the front light, and FIG. 9C is a perspective view of a rear
surface of a light-guide plate 901.
[0096] As shown in FIG. 9A, a light source 902 is disposed at a
side surface 901a of a light-guide plate 901, and a reflector 903
is provided at the back of the light source 902. A light scattering
body 904 is provided to be in contact with a lower surface of the
light-guide plate 901.
[0097] The light-guide plate 901 is a flat plate made of
transparent material in which a short side is much shorter than a
long side among four side surfaces. As the material of the
light-guide plate 901 has a transmissivity (total light
transmissivity) of 80%, preferably 85% or more, to visible light
and the refractive index is larger than 2.sup.1/2, light of an
incident angle of 90 degrees to the light-guide plate 901 can be
refracted at the side surface 901a and can be guided to the inside
of the light-guide plate 901. In this embodiment, a material with
the refractive index within the range of 1.4 to 1.7 is used.
[0098] As such transparent materials, a material such as quartz,
glass, or plastic can be used. As the plastic, a material such as
methacrylate resin, polycarbonate, polyarylate, AS resin
(acrylotrile, styrene polymer), or MS resin (methyl methacrylate,
styrene polymer) can be used as a single substance or a
mixture.
[0099] As the light source 902, a cold cathode tube or an LED is
used, and is disposed along the side 901a of the light-guide plate
901. Two light sources may be provided along a side surface
902b.
[0100] Next, the light scattering body 904 is formed by etching
after a transparent film is formed on the light-guide plate 901. As
the material for forming the transparent film, organic resin such
as polycarbonate, acryl resin, polyimide, polyamide or BCB
(benzocyclobutene); indium oxide, tin oxide, or zinc oxide is used
to form a film, or a compound film of a combination of these is
used. It is preferable that the thickness (H) of the film is made
to have the relation of H.gtoreq.2 W1 with respect to the pitch
(W1) of the light scattering body.
[0101] When the front light formed in the manner as described above
is provided between a liquid crystal panel (LCD) 905 and a user, a
liquid crystal display with high extracting efficiency of light can
be obtained.
[0102] In this embodiment, since the liquid crystal panel is
irradiated after light is reflected by the side surface of the
light scattering body, an incident angle to the liquid crystal
panel can be made small. As a result, since the component of light
which vertically illuminates the pixel electrode of the liquid
crystal panel becomes large, the light can be effectively used.
[0103] Incidentally, FIG. 9C is a view showing a trapezoid section
obtained when the light scattering body 904 is cut in the direction
of x-x'. When acute angles of the trapezoid light scattering body
904 are made .theta.5 and .theta.6, it is desirable that these
angles are large. If .theta.5 and .theta.6 are made large, it is
possible to facilitate collection of outgoing light in the
direction from the front light to the liquid crystal panel.
[0104] Incidentally, it is not necessary that the angels .theta.5
and .theta.6 are made the same angle, but may be different from
each other.
[0105] Besides, in this embodiment, the transparent film is newly
formed on the light-guide plate 901, and the light scattering body
904 is formed by etching the newly formed transparent film .
However, a structure as shown in FIG. 11A may be formed by directly
etching the surface (at the side of the liquid crystal panel) of
the light-guide plate 901.
Embodiment 7
[0106] Next, an example in which the present invention is used for
a back light will be described. FIGS. 10A to 10C are views showing
the structure of a back light. FIG. 10A shows a section of the back
light, and FIG. 10B is a perspective view of the back light.
[0107] As shown in FIG. 10A, a light source 1002 is disposed at a
side surface 1001a of a light-guide plate 1001, and a reflector
1003 is provided at the back of the light source 1002. A light
scattering body 1004 is provided to be in contact with an upper
surface of the light-guide plate 1001.
[0108] Thus, after light emitted from the light source 1002 passes
through the light scattering body 1004 from the light-guide plate
1001, the light irradiates a liquid crystal panel (LCD) 1005.
[0109] As the light source 1002, similarly to the case of the front
light, a cold cathode tube or an LED is used, and is disposed along
the side surface 1001a of the light-guide plate 1001. Two light
sources may be provided so as to be opposite to each other along a
side surface 1002b.
[0110] Besides, in this embodiment, after the transparent film is
newly formed on the light-guide plate 1001, the light scattering
body 1004 is formed by etching the transparent film. However, a
structure as shown in FIG. 11B may be formed by directly etching
the light-guide plate 1001 itself.
Embodiment 8
[0111] In this embodiment, a description will be given of a subject
as to current-voltage characteristics of a region in which a
current controlling TFT is to be driven, in a case where a
self-light emitting device of the present invention is operated in
digital driving.
[0112] In an EL element, if an applied voltage is changed even if
the change is slight, a current flowing through the EL element is
largely changed exponentially. From another point of view, even if
the current flowing through the EL element is change, the value of
the voltage applied to the EL element is not changed very much. The
brightness of the EL element becomes high almost in proportion to
the current flowing through the EL element. Thus, when the
brightness of the EL element is controlled by controlling the
magnitude (current value) of the current flowing through the EL
element rather than by controlling the magnitude (voltage value) of
the voltage applied to the EL element, the influence of
characteristics of a TFT is low, and the control of brightness of
the EL element is easy.
[0113] Reference will be made to FIGS. 12A and 12B. FIG. 12A shows
only structural portions of a current controlling TFT 108 and an EL
element 110 in a pixel of an EL display of the present invention
shown in FIG. 3. FIG. 12B shows current-voltage characteristics of
the current controlling TFT 108 and the EL element 110 shown in
FIG. 12A. Incidentally, a graph of the current-voltage
characteristics of the current controlling TFT 108 shown in FIG.
12B shows the magnitude of current flowing through the drain of the
current controlling TFT 108 with respect to voltage V.sub.DS
between the source region and the drain region, and FIG. 12B shows
a plurality of graphs in which values of V.sub.GS of the voltage
between the source region and the gate electrode of the current
controlling TFT 108 are different from one another.
[0114] As shown in FIG. 12A, a voltage applied between a pixel
electrode and a counter electrode 111 of the EL element 110 is made
V.sub.EL, and a voltage applied between a terminal 2601 connected
to a power supply line and the counter electrode 111 of the EL
element 110 is made V.sub.T. The value of V.sub.T is fixed by the
potential of the power supply line. Besides, a voltage between the
source region and the drain region of the current controlling TFT
108 is made V.sub.DS, and a voltage between a wiring line 2602
connected to the gate electrode of the current controlling TFT 108
and the source region, that is, a voltage between the gate
electrode and the source region of the current controlling TFT 108
is made V.sub.GS.
[0115] The current controlling TFT 108 may be either of an
n-channel TFT and a p-channel TFT.
[0116] The current controlling TFT 108 and the EL element 110 are
connected in series with each other. Thus, values of currents
flowing through both elements (the current controlling TFT 108 and
the EL element 110) are equal to each other. Accordingly, the
current controlling TFT 108 and the EL element 110 shown in FIG.
12A are driven at an intersection point (operating point) of the
graphs showing the current-voltage characteristics of both the
elements. In FIG. 12B, V.sub.EL becomes a voltage between the
potential of the counter electrode 111 and the potential at the
operating point. The voltage V.sub.DS becomes a voltage between the
potential at the terminal 2601 of the current controlling TFT 108
and the potential at the operating point. That is, V.sub.T is equal
to the sum of V.sub.EL and V.sub.DS.
[0117] Here, a case where V.sub.GS is changed is considered. As is
understood from FIG. 12B, as .vertline.V.sub.GS-V.sub.TH.vertline.
of the current controlling TFT 108 becomes large, in other words,
.vertline.V.sub.GS.vertline. becomes large, the value of the
current flowing through the current controlling TFT 108 becomes
large. Incidentally, V.sub.TH is a threshold voltage of the current
controlling TFT 108. Thus, as is understood from FIG. 12B, when
.vertline.V.sub.GS.vertline. becomes large, the value of the
current flowing through the EL element 110 at the operating point
naturally becomes large. The brightness of the EL element 110
becomes high in proportion to the value of the current flowing
through the EL element 110.
[0118] When .vertline.V.sub.GS.vertline. becomes large so that the
value of the current flowing through the EL element 110 becomes
large, the value of V.sub.EL also becomes large in accordance with
the value of the current. Since the magnitude of V.sub.T is
determined by the potential of the power supply line, when V.sub.EL
becomes large, V.sub.DS becomes small by that.
[0119] As shown in FIG. 12B, the current-voltage characteristics of
the current controlling TFT is divided into two regions with
respect to the values of V.sub.GS and V.sub.DS. A region of
.vertline.V.sub.GS-V.sub.TH.-
vertline.<.vertline.V.sub.DS.vertline. is a saturation region,
and a region of
.vertline.V.sub.GS-V.sub.TH.vertline.>.vertline.V.sub.DS.ver-
tline. is a linear region.
[0120] In the saturation region, the following expression 4 is
established. Incidentally, I.sub.DS is a value of current flowing
through a channel formation region of the current controlling TFT
108. Besides, .beta.=.mu.C.sub.oW/L, .mu. is a mobility of the
current controlling TFT 108, C.sub.o is gate capacity per unit
area, and W/L is a ratio of a channel width W to a channel length L
of the channel formation region.
I.sub.DS=.beta.(V.sub.GS-V.sub.TH).sup.2/2 [Expression 4]
[0121] In the linear region, the following expression 5 is
established.
I.sub.DS=.beta.{(V.sub.GS-V.sub.TH)V.sub.DS-V.sub.DS.sup.2/2}
[Expression 5]
[0122] As is understood from the expression 4, in the saturation
region, the current value is hardly changed by V.sub.DS, but the
current value is determined by only V.sub.GS.
[0123] On the other hand, as is understood from the expression 5,
in the linear region, the current value is determined by V.sub.DS
and V.sub.GS. When .vertline.V.sub.GS.vertline. is made large, the
current controlling TFT comes to operate in the linear region.
Then, V.sub.EL also gradually becomes large. Thus, V.sub.DS becomes
small by the increase of V.sub.EL. In the linear region, when
V.sub.DS becomes small, the amount of current also becomes small.
Thus, even if .vertline.V.sub.GS.vertline. is made large, the
current value becomes hard to increase. When
.vertline.V.sub.GS.vertline.=.infin., current value=I.sub.MAX. That
is, even if .vertline.V.sub.GS.vertline. is made large, current
larger than I.sub.MAX does not flow. Here, I.sub.MAX is a value of
current flowing through the EL element 110 when
V.sub.EL=V.sub.T.
[0124] Like this, by controlling the magnitude of
.vertline.V.sub.GS.vertl- ine., the operating point can be placed
in the saturation region or the linear region.
[0125] Although it is desirable that the characteristics of all
current controlling TFTs are ideally identical to one another,
actually, the threshold value V.sub.TH and the mobility .mu. are
often different among the respective current controlling ITFs. When
the threshold value V.sub.TH and the mobility .mu. of the
respective current controlling TFTs are different from one another,
as is understood from the expressions 4 and 5, the value of the
current flowing through the channel formation region of the current
controlling TFT 108 becomes different even if the value of V.sub.GS
is the same.
[0126] FIG. 13 shows current-voltage characteristics of a current
controlling TFT in which a threshold value V.sub.TH and a mobility
.mu. deviate. A solid line 1701 is a graph of ideal current-voltage
characteristics, and solid lines 2702 and 2703 respectively
indicate current-voltage characteristics of the current controlling
TFT in the case where the threshold value V.sub.TH and the mobility
.mu. become different from ideal values. It is assumed that the
graphs 2702 and 2703 of the current-voltage characteristics deviate
from the graph 2701 of the current-voltage characteristics having
the ideal characteristics by the same current value .DELTA.I.sub.1
in the saturation region, an operating point 2705 of the graph 2702
of the current-voltage characteristics is in the saturation region,
and an operating point 2706 of the graph 2703 of the
current-voltage characteristics is in the linear region. In that
case, when deviations between a current value at an operating point
2704 of the graph 2701 of the current-voltage characteristics
having the ideal characteristics and current values at the
operating point 2705 and the operating point 2706 are respectively
made .DELTA.I.sub.2 and .DELTA.I.sub.3, the operating point 2706 in
the linear region is smaller than the operating point 2705 in the
saturation region.
[0127] Thus, in the case where the driving method of the digital
system described in the present invention is used, when the current
controlling TFI and the EL element are driven so that the operating
point exists in the linear region, it is possible to carry out a
gradation display suppressing uneven brightness of the EL element
due to deviation of characteristics of the current controlling
TFT.
[0128] In the case of conventional analog driving, it is preferable
to drive the current controlling TFT and the EL element so that the
operating point exists in the saturation region in which the
current value can be controlled by only
.vertline.V.sub.GS.vertline..
[0129] As a summary of the above operation analysis, FIG. 14 shows
a graph of the current value with respect to the gate voltage
.vertline.V.sub.GS.vertline. of the current controlling TFT. When
the .vertline.V.sub.GS.vertline. is made large and becomes larger
than the absolute value .vertline.V.sub.TH.vertline. of the
threshold voltage of the current controlling TFT, the current
controlling TET comes to have a conductive state, and current
starts to flow. In the present specification,
.vertline.V.sub.GS.vertline. at this time is called a lighting
start voltage. When .vertline.V.sub.GS.vertline. is further made
large, .vertline.V.sub.GS.vertline. becomes a value (here, it is
temporarily made A) so that
.vertline.V.sub.GS-V.sub.TH.vertline.=.vertli-
ne.V.sub.DS.vertline. is satisfied, and a saturation region becomes
a linear region. Further, when .vertline.V.sub.GS.vertline. is made
large, the current value becomes large and the current value
becomes saturated. At that time,
.vertline.V.sub.GS.vertline.=.infin..
[0130] As is understood from FIG. 14, in the region of
.vertline.V.sub.GS.vertline..ltoreq..vertline.V.sub.TH.vertline.,
current hardly flows. The region of
.vertline.V.sub.TH.vertline..ltoreq..vertline-
.V.sub.GS.vertline..ltoreq.A is the saturation region, and the
current value is changed by .vertline.V.sub.GS.vertline.. The
region of A.ltoreq..vertline.V.sub.GS.vertline. is the linear
region, and the value of the current flowing through the EL element
is changed by .vertline.V.sub.GS.vertline. and
.vertline.V.sub.DS.vertline..
[0131] In the case where the self-light emitting device of the
present invention is operated by the digital driving, it is
preferable to use the region of
.vertline.V.sub.GS.vertline..ltoreq..vertline.V.sub.TH.vertline- .
and the linear region of A.ltoreq..vertline.V.sub.GS.vertline..
Incidentally, this embodiment can be freely combined with the
self-light emitting device described in the embodiments 1 to 3.
Embodiment 9
[0132] In the case of self-emission device of the present
invention, an external light emitting quantum efficiency can be
remarkably improved by using an EL material by which
phosphorescence from a triplet exciton can be employed for emitting
a light. As a result, the power consumption of the EL element can
be reduced, the lifetime of the EL element can be elongated and the
weight of the EL element can be lightened.
[0133] The following is a report where the external light emitting
quantum efficiency is improved by using the triplet exciton (T.
Tsutsui, C. Adachi, S. Saito, Photochemical processes in Organized
Molecular Systems, ed. K. Honda, (Elsevier Sci. Pub., Tokyo, 1991)
p. 437).
[0134] The molecular formula of an EL material (coumarin pigment)
reported by the above article is represented as follows.
Chemical Formula 1
[0135] (M. A. Baldo, D. F. O Brien, Y. You, A. Shoustikov, S.
Sibley, M. E. Thompson, S. R. Forrest, Nature 395 (1998) p.
151)
[0136] The molecular formula of an EL material (Pt complex)
reported by the above article is represented as follows.
Chemical Formula 2
[0137] (M. A. Baldo, S. Lamansky, P. E. Burrows, M. E. Thompson, S.
R. Forrest, Appl. Phys. Lett., 75 (1999) p. 4.)
[0138] (T. Tsutsui, M. -J. Yang, M. Yahiro, K. Nakamura, T.
Watanabe, T. Tsuji, Y Fukuda, T. Wakimoto, S. Mayaguchi, Jpn, Appl.
Phys., 38 (12B) (1999) L1502)
[0139] The molecular formula of an EL material (Ir complex)
reported by the above article is represented as follows.
Chemical Formula 3
[0140] As described above, if phosphorescence from a triplet
exciton can be put to practical use, it can realize the external
light emitting quantum efficiency three to four times as high as
that in the case of using fluorescence from a singlet exciton in
principle. In self-emission device shown in Embodiments 1 to 5, the
structure according to this embodiment can be performed and freely
implemented in combination of any structures of the present
invention.
Embodiment 10
[0141] The self-emission device formed according to the present
invention, is a self light emitting type, therefore compared to a
liquid crystal display device, it has excellent visible properties
and is broad in an angle of visibility. Accordingly, the
self-emission device can be applied to a display portion in various
electronic devices. For example, in order to view a TV program or
the like on a large-sized screen, the self-emission device in
accordance with the present invention can be used as a display
portion of an EL display device (a display equipped with a
self-emission device in the case) having a diagonal size of 30
inches or larger (typically 40 inches or larger).
[0142] The EL display includes all kinds of displays to be used for
displaying information, such as a display for a personal computer,
a display for receiving a TV broadcasting program, a display for
advertisement display. Moreover, the self-emission device in
accordance with the present invention can be used as a display
portion of other various electric devices.
[0143] As other electronic equipments of the present invention
there are: a video camera; a digital camera; a goggle type display
(head mounted display); a car navigation system; a sound
reproduction device (a car audio stereo, an audio set and so
forth); a notebook type personal computer; a game apparatus; a
portable information terminal (such as a mobile computer, a
portable telephone, a portable game machine, or an electronic
book); and an image playback device equipped with a recording
medium (specifically, device provided with a display portion which
plays back images in a recording medium such as a digital versatile
disk Player (DVD), and displays the images). In particular, in the
case of the portable information terminal, use of the self-emission
device is preferable, since the portable information terminal that
is likely to be viewed from a tilted direction is often required to
have a wide viewing angle.
[0144] Further, these electronic device can be mounted the light
sensor which can control the brightness corresponding to
surrounding brightness to lower the electronic power consumption.
It is preferable that the contrast of brightness of the
self-emission device to surrounding brightness is set from 100 to
150. FIGS. 15A to 16B respectively show various specific examples
of such electronic devices.
[0145] FIG. 15A shows an EL display containing a casing 2001, a
support stand 2002, and a display portion 2003. The present
invention can be used as the display portion 2003. Such an EL
display is a self-emission type so that a back light is not
necessary. Thus, the display portion can be made thinner than that
of a liquid crystal display.
[0146] FIG. 15B shows a video camera, and contains a main body
2101, a display portion 2102, a sound input portion 2103, operation
switches 2104, a battery 2105, and an image receiving portion 2106.
The self-emission device of the present invention can be used as
the display portion 2102.
[0147] FIG. 15C shows a portion (the right-half piece) of an EL
display of head mount type, which includes a main body 2201, signal
cables 2202, a head mount band 2203, a display portion (a) 2204, an
optical system 2205, a display portion (b) 2206, or the like. The
electronic device and the driving method of the present invention
is applicable to the display portion (a) 2204 or the display
portion (b) 2206.
[0148] FIG. 15D shows an image playback device equipped with a
recording-medium (specifically, a DVD playback device), and
contains a main body 2301, a recording medium (such as a DVD) 2302,
operation switches 2303, a display portion (a) 2304, and a display
portion (b) 2305. The display portion (a) 2304 is mainly used for
displaying image information. The display portion (b) 2305 is
mainly used for displaying character information. The self-emission
device of the present invention can be used as the display portion
(a) 2304 and as the display portion (b) 2305. Note that the image
playback device equipped with the recording medium includes devices
such as image playback devices and game machines.
[0149] FIG. 15E shows a portable (mobile) computer, and contains a
main body 2401, a camera portion 2402, an image receiving portion
2403, operation switches 2404, and a display portion 2405. The
self-emission device of the present invention can be used as the
display portion 2405.
[0150] FIG. 15F is a personal computer, and contains a main body
2501, a casing 2502, a display portion 2503, and a keyboard 2504.
The self-emission device of the present invention is applicable to
the display portion 2503.
[0151] Note that if the luminance of organic EL materials increases
in the future, then it will become possible to use the present
invention in a front type or a rear type projector by expanding and
projecting light containing output image information with a lens or
the like.
[0152] Further, the above electric devices display often
information transmitted through an electronic communication circuit
such as the Internet and CATV (cable tv), and particularly
situations of displaying moving images is increasing. The
self-emission device is suitable for displaying moving pictures
since the EL material can exhibit high response speed. However, if
the contour between the pixels becomes unclear, the moving pictures
as a whole cannot be clearly displayed. Since the self-emission
device in accordance with the present invention can make the
contour between the pixels clear, it is significantly advantageous
to apply the self-emission device of the present invention to a
display portion of the electronic devices.
[0153] In addition, since the self-emission device conserves power
in the light emitting portion, it is preferable to display
information so as to make the light emitting portion as small as
possible. Consequently, when using the self-emission device in a
display portion mainly for character information, such as in a
portable information terminal, in particular a portable telephone
or a sound reproduction device, it is preferable to drive the light
emitting device so as to form character information by the light
emitting portions while non-light emitting portions are set as
background.
[0154] FIG. 16A shows a portable telephone, and contains a main
body 2601, a sound output portion 2602, a sound input portion 2603,
a display portion 2604, operation switches 2605, and an antenna
2606. The self-emission device of the present invention can be used
as the display portion 2604. Note that by displaying white color
characters in a black color background, the display portion 2604
can suppress the power consumption of the portable telephone.
[0155] FIG. 16B shows a sound reproduction device, in a concrete
term, a car mounted audio equipment and contains a main body 2701,
a display portion 2702, and operation switches 2703 and 2704. The
self-emission device of the present invention can be used as the
display portion 2702. Further, a car mount type audio stereo is
shown in this embodiment, but a fixed type audio playback device
may also be used. Note that, by displaying white color characters
in a black color background, the display portion 2704 can suppress
the power consumption. It is effective to portable sound
reproduction device.
[0156] As described above, the application range of this invention
is extremely wide, and it may be used for electric devices in
various fields. Further, the electric device of this embodiment may
be obtained by using a self-emission device freely combining the
structures of the first to eighth embodiments.
[0157] When the present invention is carried out to provide a light
scattering body on an insulator, extracting efficiency of light
from a light emitting element, especially in an EL element can be
improved. Further, when a transparent film is etched to form the
light scattering body, minute processing of pitches becomes
possible. When the light scattering body of minute pitches is
formed with the manner described above, the self-light emitting
device with high efficiency of light emission can be provided.
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